1. Field of the Invention
The present invention relates to an ozone producing apparatus. More particularly, it relates to an ozone producing apparatus for continuously producing ozone and storing the same in an adsorbed state and supplying the ozone when required by desorbing (separating) the same.
2. Description of the Related Art
While a large quantity of cooling water is used at power stations and in chemical industries, microorganisms or seaweed in the water cause slime hazards and thereby resulting in blockage of canals or deterioration of heat exchange efficiency. One method which might be taken as a countermeasure to prevent such troubles is to employ ozone water of high density. In order to produce high density ozone water, it is more advantageous to employ a so-called intermittent ozone producing method, wherein a small sized ozone generator of small capacity is used to store the produced ozone by using an adsorbent over a long period and to take this stored ozone out from the adsorbent when required for producing high density ozone water, rather than producing ozone with an ozone generator of large capacity, in view of initial and running costs.
An ozone producing apparatus employing such an ozone producing method is known to comprise the following components as shown in FIG. 10: an ozone generator 50, an oxygen supply source 51, a circulating blower 52, an adsorption/desorption tower 53, a cooling source 54, a heating source 55, a water flow ejector 56 and switch valves 57a to 57g. The adsorption/desorption tower 53 is of a double cylinder type of which an inner cylinder is filled with an ozone absorbent and an outer cylinder with heating medium. Silica gel might be employed as the ozone absorbent, and ethylene glycol or an alcohol group as the heating medium. It should be noted that the circulating blower 52, ozone generator 50 and adsorption/desorption tower 53 constitute, in this order, a circulating system.
Operations of the apparatus will now be explained. There are two operations in total, namely ozone adsorbing operation, and ozone desorbing operation.
The adsorbing operation will first be explained. Oxygen is supplied by the oxygen supply source 51 so that the pressure in the circulating system is always constant. In this case, the pressure is normally maintained at 1.5 kg/cm.sup.2. When oxygen is made to flow in the circulating system by the circulating blower 52 while the switch valves 57c and 57d are in an opened condition, a part of the oxygen is converted into ozone to generate an ozonized oxygen while passing through the discharge space of the ozone generator 50, and the ozonized oxygen is then transferred to the adsorption/desorption tower 53. The adsorbent in the adsorption/desorption tower 53 selectively adsorbs ozone, and the remaining oxygen is returned to the circulating blower 52 through the switch valve 57c. Oxygen which has been consumed as ozone to be absorbed is supplemented through the oxygen supply source 51. Since the adsorbent assumes a property that adsorption capacity of ozone varies depending on temperature, the absorbent is cooled by the cooling source 54 to not more than -30.degree. C. That is, the lower the temperature becomes, an amount of ozone absorption increases, while the higher the temperature becomes, it decreases. Accordingly, the temperature of absorbent is raised by the heating source 55 when desorbing ozone.
When the adsorbent in the adsorption/desorption tower 53 has adsorbed ozone to approach the ozone saturation adsorption amount, the desorbing operation of ozone is performed. In the desorbing operation, operations of the ozone generator 50, circulating blower 52 and cooling source 54 are terminated and the switch valves 57a to 57d are closed. Thereafter, the heating source 55 and water flow ejector 56 start their operation and switch valves 57e to 57g are opened. At this time, temperature of the adsorbent is raised by applying heat through the heating source 55 so that ozone which has been adsorbed by the adsorbent can easily be desorbed therefrom. By depressing to suck ozone in the adsorption/desorption tower 53 by means of the water flow ejector 56, ozone is dispersed into water in the water flow ejector 56 to be dissolved and sent to, as ozone water, places where it is used. When the desorbing period is completed in this way, the process returns to the initial adsorbing operation and is continuously repeated.
In preventing slime adhesion, it is important to perform treatment with high density ozone in a short time. In other words, the maximum peak density of the desorbed ozone becomes important. However, the density of ozone water can not be stabilized with a conventional apparatus as shown in FIG. 10, since the ozone desorption density decreases with a time lapse for desorption, and when a density exceeding a specified density is required for a specified period, ozone can not be effectively used. That is, when employed for slime prevention, not all of the adsorbed and stored ozone can be desorbed in a short time to be injected in a pulse-like manner, and after the density of desorbed ozone reaches a peak density, ozone of low density which is not so much effective in preventing adhesion of slime is desorbed. As discussed earlier, this is not only uneconomical but might also generate oxidants when applied to sea water which badly effect marine products. Further, there also exists a drawback that a huge amount of energy is consumed at the time of storing ozone, since the adsorbent needs to be cooled when adsorbing ozone and the adsorbent needs to be heated when desorbing ozone.
There has been proposed an intermittent-type ozone supplying apparatus, in contrast to such an apparatus described above, in which a canal for adsorbing and supplying ozone is provided with a by-pass circuit including switch valves and channel resistance (refer to Japanese Examined Patent Publication No. 284/1990). However, although such a supplying apparatus is capable of maintaining density of ozone water, it is difficult to generate ozone water of high density therewith.
On the other hand, there is known an intermittent-type ozone supplying apparatus in which a serpentine the pipe is disposed in an inner cylinder for raising the temperature of the adsorbent (refer to Japanese Examined Patent Publication No. 34484/1985). However, such a supplying apparatus presents drawbacks that oxygen-containing gas (with an oxygen density of not less than 80 wt %) from the ozone generator remains in the adsorption/desorption tower immediately before the desorption is performed, and that desorption by heating alone requires a long time for treatment so that the amount of decomposed ozone during this time becomes also high, whereby this apparatus is not suitable for efficiently desorbing stored ozone in a short time, and ozone of low density also is desorbed in the latter half of the desorbing process which is difficult to be injected in a pulse-like manner.
The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an economical ozone producing apparatus which is capable of decreasing the amount of energy required at the time of storing ozone, and with which little byproducts such as oxidants are generated by enabling definite ozone injection, that is, taking out stored ozone of high density as much as possible in a short time.